Projectors used in daily life are manufactured based on 3LCD, Digital Light Processing (DLP) or Liquid Crystal on Silicon (LCoS) technology. Although the color models and projection principles are different from each other, these technologies separate white light beams from high voltage halogen lamps or mercury vapor lamps into red (R), green (G) and blue (B) beams by dichronic mirrors, panels or color wheels. However, as to requirement of portability for every device people use in daily life, bulky size of the projectors manufactured by the projection methods with traditional lamps can not be further reduced. Therefore, it is inevitable to use light emitting diode (LED) or visible laser diode (LD) to replace the traditional lamps as a solution for miniaturized projectors.
Recently, projector manufacturers start to use three-primary-color (RGB) LED or visible LD. LED or visible LD has small volume. By using DLP and LCoS technologies with these light sources, lighting devices can be effectively simplified so that the projector can be more compact. Meanwhile, LED or visible LD has more advantages that traditional lamps don't have. For example, LED or visible LD can be switched on swiftly, operate noiselessly and have longer lifetime so that user doesn't have to change LED or visible LD often.
A visible laser is a laser with a beam that can be seen by the naked eye. Through a process known as stimulated emission, laser releases light beams, or electromagnetic radiation. Essentially, an electron is stimulated and moves to an area of lower energy. The energy lost takes the form of a photon, a unit of electromagnetic radiation, and is emitted in the form of a laser beam. Laser light is usually spatially coherent, which means that the light either is emitted in a narrow, low-divergence beam, or can be converted into one with the help of optical components such as lenses. Hence, compared with LED, a visible laser diode can emit beams for a longer transmission distance. Images sent via laser beams are not interfered with a multi-directional light source. Therefore, mini projectors (or called pico projectors) often use visible laser diodes as a light source.
Several inventions disclose designs of a projecting system using laser diodes as a light source. Please refer to FIG. 1. U.S. Pat. No. 7,252,394 provides a projection display system which includes a light source emitting a light beam, and a reflecting mirror system for scanning the light beam over an image to illuminate the image. The light source can be a solid state device such as a laser diode. The reflecting mirror system can be one or more MEMS scanning mirrors that rotate to raster scan the light beam over the image. The image can be an advertisement located on a wall, a screen, a sign, or a billboard. The image can also be a semi-transparent image that is projected onto a medium to produce a larger image. The reflecting mirror system has one vertically scanning mirror and at least one horizontally scanning mirror. Hence, a raster scanning over one complete screen or more discrete tiles can be achieved. However, although only one vertically scanning mirror is able to perform raster scanning, it is hard to coordinate other horizontally scanning mirrors with the vertically scanning mirror. For a screen composed of several tiles, there would be many malpositions or even tile overlapping occurred due to the problem. When the device is slightly shocked, the whole screen will become unstable as well.
FIG. 2 shows U.S. Pat. No. 7,209,271. '271 provides a display apparatus which includes a scanning assembly that scans about two or more axes, typically in a raster pattern. A number of light sources emit light from spaced apart locations toward the scanning assembly so that the scanning assembly simultaneously scans more than one of the beams. The light sources are positioned so that their beams each illuminate discrete regions of the image field that are substantially non-overlapping with respect to the other discrete regions. The image is thus formed from a set of tiles. By activating a first light source during a forward sweep of the mirror and activating a second light source during a reverse sweep of the mirror, a common line can be written during a single sweep of the mirror. Shifting the position of the sources such that the two halves are aligned reduces raster pinch. The invention points out the problem of raster pinch effect and provides a solution to it. However, the modulator for controlling color model has heavy work load. The device can not work properly under slight shock.
The objects of the present invention are to solve the problems mentioned above. Meanwhile, it has effect to reduce modulation speed. Each modulator can have a longer life time and be easily repaired.